This once-grand marvel of engineering is now 41 miles of scenic hiking trail.

Decades after testing the polio vaccine on unwitting patients, this historic mental hospital sits in ruin.

This Queens hospital has stood abandoned for almost 20 years after its patients were secretly relocated in the dead of night.

These World War I shooting range tunnels are now haunted halls of underground graffiti accessed through the roots of a tree.

This former theme park in New York's Adirondack Mountains fell into ruin before being resurrected as a state-run campground

This old cement mine has been used as everything from a mushroom farm to a recording studio.

The abandoned grounds and derelict greenhouses of this once-magnificent Edwardian estate are now a nature preserve open for exploration.

Hundreds of numbered stakes hidden in the woods mark the graves of the lost souls of a nearby asylum.